This invention relates to the pyrometallurgical treatment of non-ferrous sulfide material. More particularly, it relates to the smelting or converting of particulate non-ferrous sulfide material, such as nickel or copper sulfide. In the claimed process, particulate sulfide material is injected into a reaction vessel below the surface of a melt. Top blowing with an oxygen-containing gas generates heat and brings about the oxidation of the sulfides with a significant reduction in the amount of dust generated.
One currently practiced method for treating sulfide ore concentrates is by flash smelting/converting in which the sulfur and iron content of the ore is burned while the concentrate is suspended in the oxidizing medium. This method permits economical treatment of the furnace off-gas to recover a substantial part of the liberated sulfur content.
A serious drawback to flash operations is the generation of substantial amounts of dust, which must be removed in the gas cleaning system prior to further treatment for recovery of sulfur dioxide. In contrast, injection of the sulfide material below the bath surface results in a substantial decrease in the amount of dust produced.
In flash smelting/converting, the heat of combustion is generated in the free board of the furnace and can lead to overheating of the refractory. In the process of the invention, which utilizes top blowing technology, heat is generated on the bath surface away from the walls of the reaction vessel. An additional embodiment of the invention utilizes non-reactive gas sparging as a bottom stirring mechanism. The stirring of the bath created by the gas sparging distributes this heat, causing the bath to reach a uniform temperature. Thus, damage to the refractory is significantly reduced. Furthermore, it is likely that the reactor used for the present process (usually of the Pierce-Smith converter type because of the ease of retrofitting) will have a higher specific capacity than a flash reactor.
The top blowing process alone is not without its disadvantages. Though oxygen efficiency is high, it may be less than the 100% achieved during flash reaction. However, when the top blowing process is utilized in conjunction with particulate injection below the bath surface, it was surprisingly found that the overall economics of this unique process were superior to those of flash reaction. This is particularly true when the problem of dust generation is considered. For example, when treating chalcocite, flash converting results in up to 15% of fed copper ending up as dust. The submerged injection of chalcocite would reduce this amount considerably.
Suggestions have been made in the past to inject solids below the melt surface in combination with submerged blowing with air or oxygen-enriched air. While this prior art method, taught by U.S. Pat. No. 3,281,236 to Meissner, would reduce the dusting caused by flash reaction, there are significant drawbacks. There would be additional fuel requirements due to the lower level of oxygen enrichment and a larger, more costly gas cleaning system to handle the resulting higher off-gas rates. Were tonnage oxygen to be used in such a process, shrouded tuyeres would be required. Furthermore, these processes are known to suffer from excessive refractory and tuyere wear.
The desirability of using "top blowing/bottom stirring" technology in a preferred embodiment, as compared to simply blowing with oxygen-containing gas, was first demonstrated by Marcuson et al with respect to the conversion of white metal copper in U.S. Pat. No. 4,830,667. The additional use of bottom stirring, along with top blowing and submerged particulate injection, would further assist in overcoming the above problems. Bottom stirring increases the circulation of the molten bath to allow for increased contact with the top blown oxygen. Thus, lance and vessel design are simplified and less costly, and reaction efficiency is increased.